Gun Firing help?

Hi huys, I followed a guide on here about how to make a gun fire, and it gave me this javascript code:

 var prefabBullet = gameObject;
 function Update() { if(Input.GetButton("Fire1")){
 bullet = Instantiate(prefabBullet; gameObject.Find("spawn").transform.position;
 bullet.rigidbody.AddForce(transform.forward * Speed);
 }
 }

I have a prefab of a square gameObject named prefabBullet, but i keep getting an error saying that the code has an "unexpected token 'prefabBullet'". I'm not quite sure what it wrong here, so any help would be much appreciated thanks.